I've had some black goo problems. One of the things I'm planning now, is to go back to regular 2-stroke oil. I don't think the synthetic varieties completely burn, or at least none that I have tried seem to. This leaves the black goo around.
I made one huge mistake of taking some advice and running some synth at double the recommended mix and about one gallon or less later, I suddenly had no start issues. This happened on three different engines. I did two EI upgrades, they ran a bit again and then after a few flights, they wouldn't start and run again. Finally, after pulling my hair out and a friend reading on a thread in here somewhere, I looked inside the plug hole and discovered a nice layer of black goo on the piston crown. I took one engine apart and cleaned it completely with brake kleen. Lubed it up good, put it back together, started running my new mix and no problems since. Note that the muffler needed to be cleaned as well, as the black goo was still getting on the plane. (sorry can't help with WB cleaning, but Plexus works great on plastic coverings... or any plexiglas cleaner polish for M/C helmet visors. It cleans and polishes and everything looks new again. The polish it leaves behind, makes the next cleaning even easier.)
Then, for the second one, I thought I could clean it through the plug hole, as brake kleen removed the stuff easily, with just a little brushing with a flux brush. I got it all shiney clean inside, but still struggled. So, after more grief and just not knowing, I took that one apart and did the same as the first. Same result... all cleaned up and running great.
The third engine seems to have uber spark and for whatever reason seems to be dealing with the goo better. So, I did the plug hole clean on it and have had success. Maybe it just didn't have as much gas through it. I can't really say.
My flying friend has been through the same problems now. Geez... it's 2010, you'd think they'd know how to make good 2-stroke oil by now?
Either way, I'm going back to something that 'burns'. I think the synth stuff is designed to not burn, but stay there (a good 'theory'). The one thing that is 'very' different with our use of these engines, and something that in particular the carbs were never designed to do, is that we are mostly running in mid-range. Think about it. Most 2-stroke engines with walbro like carbs are supposed to start and idle, and then normally they run at wide open... chainsaw, weedeater, leaf blower, etc. Idle a bit, then work a while wide open. With the bulk of the running at wide open, perhaps these synth oils just get blown out or whatever and do work well for those situations? In the case of motorcycles and such, the carbs and oil systems are pretty advanced versus what we run.
Also of note... changing oils can greatly change the power of the fuel. This is about the oil burning or not. So, select something... pick a ratio... be particular to replicate that every time and tune your engines with that mix. The power difference becomes obvious during a pull out from 3d hovering with a 40%er.
I did run across one supplier of gassers that seemed to feel the same way on this. For most of our engines, the best 2-stroke non-synth from a place like Wally World is way better than most synths. A great natural oil (I'm trying to chase down a supplier who stocks Belray at the moment) is as good as you can do. And somewhere between 30:1 and 50:1 is great. I have been doing 40:1 with no wear problems. Actually, I'm doing 3 ounces per gallon, or 42.6666:1. Most of my other recent lawn and garden machines, a Mantis and a Husky chainsaw, both recommended 50:1. I think my mix has plenty of oil as long as I run a properly tuned engine.
Do remember that a change in the oil used in the mix, does effect the power of the fuel and the tuning of the carb. Something as simple as changing your oil mix might create a lean situation and burn up an engine. One of our recent converts had to lean out their engine when going back to regular oil, which in my thinking means that switching the other way could only lead to a lean situation, as it would need to be richer to run right.
Also, oil companies love to pay for advertising. Just look at any Nascar. That really tells you a lot. Those engines only have to make it 500 miles.
Anyway, payment to engine companies 'might' influence a recommendation. Might??? Ever notice how Husky says to use only their 2-stroke oil? Lawnboy.. same deal. Some of this can be that they have picked a good oil, but they never list any 'others' that are just as good. They get to sell oil or maybe get paid to sell a particular oil.